Such measuring systems are used for example in the development and production of components of mobile radio technology. The signal analysers are for example spectrum analysers, vector signal analysers, time-domain analysers, code-domain analysers or system protocol testers. With these, in addition to the general measurements for instance of the level, of the spectrum etc., measurements are also implemented in which the received signal must be demodulated before analysis. The signal generators produce high frequency measuring signals corresponding to the transmission standard, for example GSM (global System for Mobile Communication) standard or a wideband CDMA (Code Division Multiple Access) standard for the third generation mobile radio UMTS (Universal Mobile Telecommunication Standard). In order to measure the bit error rate or the EVM (Error Vector Magnitude) or the phase or frequency shift error, it is necessary to compare the actual symbol sequence or actual bit sequence determined by the demodulation of the output signal of the test unit with the reference symbol sequence or the reference bit sequence with which the measuring signal supplied to the test unit was modulated in the signal generator.
In operating devices (mobile stations, base stations etc.), the useful data are provided with error protection data in the transmitter before modulation, said error protection data enabling an error correction for the receiver to a limited degree, i.e. the incorrectly received bits or symbols can be corrected to a limited degree.
This procedure would be possible fundamentally also with signal analysers. However, it would be disadvantageous that the signal analysers must control a large quantity of operating standards, for example both for the second generation and third generation mobile radio and it is not possible on grounds of complexity to implement the very different error correction methods of all operating standards in one universal signal analyser. In universally usable signal analysers, only universal demodulators, which cannot evaluate the error protection mechanisms, can therefore be used. Hence, in the case of universal signal analysers, the error protection methods cannot however be used for generating the reference symbol sequence or reference bit sequence, i.e. the signal cannot be analysed in all operating cases.
Even if demodulators were used in the signal analysers with the considerable complexity required therefor and which controlled the various error protection methods for all the operating standards occurring in practice, a further problem resides in the fact that measurements must also be implemented in which the test unit is supplied with a distorted signal not occurring in normal operation in order to test the test unit in boundary situations for testing the transition behaviour. For example, noise units and distortion units are present in the signal generators, which can supply the measuring signal with noise and distortion which is or are greater than the noise component occurring in normal operation or the distortion occurring in normal operation. Hence, in the measuring case, the energy per bit Eb in relation to the noise output N0 is smaller so that the error correction methods no longer permit complete correction of the bit or symbol errors and the reference bit sequence or reference symbol sequence cannot be completely reconstructed by using the error correction methods.
A further problem in the state of the art resides in the fact that synchronisation must take place with respect to various partial signal portions of the measuring signal. For example, in the case of a GSM signal, the TDMA frame (Time Division Multiple Access Frame) of which is divided into eight timeslots, must be synchronised with respect to a training sequence present in the middle of each slot as a synchronised bit sequence. In order to be able to be synchronised with respect to these training sequences, the synchronised bit sequences which the signal generator generates must be known to the signal analyser. This was only possible previously in that the synchronised bit sequences were input by hand via a keyboard into the signal analyser. This is laborious, leads to input errors and, in the case of frequent changing of the synchronised bit sequence, to a fairly long measuring time.
The object underlying the invention is therefore to produce a measuring system which is usable for the most varied of operating standards and with a high signal/noise ratio at a justifiable cost.
The object is achieved by the features of claim 1.